1. Field of the Invention
This invention relates in general to an automatic temperature control system for automobiles, improved components thereof and the arrangement of such components within the system.
2. Description of the Prior Art
Automatic temperature control systems were first introduced in about 1964 in the United States and are now available on most large size cars. In the systems heretofore, the components of the system have been scattered throughout the car, being interconnected by vacuum and wiring harnesses. One of these systems, for instance, has a main component grouping on the power servo, with other hardware located on the dash control, in ducts, on the air conditioning case, and in the engine compartment. Another has many components grouped on the heater-air conditioning case, with other components on the dash control, under the dash and in the engine compartment. These systems are generally complicated, difficult to install and maintain, expensive to produce and inaccurate.
The components of such systems and their function are as set forth below:
1. Sensors - to sample in-car and ambient temperature;
2. Transducers - to convert the sensors' output to a control signal;
3. A power servo - to convert the control signal to a stroke, thereby driving program switches and a temperature door. Bimetal sensors have been used to sense temperature changes and provide a signal responsive thereto for many years. However, the signal from such a sensor is very small and is rarely able by itself to provide the necessary force to activate a mechanical or electrical system of which the sensor is a part;
4. Program switches - to control system functions such as air discharge location, blower speed, recirculation, water valve, on-off function, etc.;
5. A temperature blend door - to modulate the air discharge temperature from the heater-air conditioning system;
6. Dash controls - contains levers used by the driver of a car to adjust and set the system to the desired mode and condition of operation;
7. Selector switches - operated by the dash controls;
8. Cold engine lockout (CELO) valve - to delay the system operation in its heater mode until the heater core is warm;
9. Compressor ambient switch - to control the compressor operation as a function of the ambient temperature;
10. A water valve - controlled by a program switch to turn water off to the heater core under maximum cooling conditions; and
11. A resistor block - contains a dropping resistor for fan speed control. This works in conjunction with the program switches.